This application relates to a method of inspecting the formation of cooling holes in a turbine airfoil.
Gas turbine engines are known and include a compressor compressing air and delivering it into a combustor where it is mixed with fuel and ignited. Products of this combustion pass downstream over turbine rotors, driving them to rotate. The turbine rotors, in turn, drive a compressor rotor.
The turbine rotors include a number of airfoils including rotating blades and static vanes. Turbine rotors, in particular, are subject to very high temperature from the products of combustion.
The turbine airfoils are typically provided with cooling channels and various cooling schemes for delivering cooling air. The airfoils are typically provided with cooling holes extending from internal cavities, which deliver cooling air to an outer skin of the airfoil. The outer skin of the airfoil is typically also provided with various coatings, as an example, a thermal barrier coating.
In quality control inspection of manufactured airfoils, many things must be checked. One thing checked is to ensure a deposited coating has not plugged any of the cooling holes. Also, even for uncoated airfoils, the inspection ensures the holes have been drilled through completely through to the internal cavities of the cooling channels, and have not been blocked by a drilling process. This may be done utilizing what is known as an infrared method. Air is injected into cooling channels within the airfoil and it leaves through the cooling holes at the outer skin. An infrared detector (such as an infrared camera) studies the location of the exit points and can tell if a particular cooling hole is plugged due to the infrared image captured from the surface.
Another quality control step that is performed is the hole true position inspection. Typically, a five axis vision based coordinate measurement machine is utilized. However, this machine typically measures the location of an outlet end of the cooling hole. A quality control system would find the location of the inlet end more important.
In addition, the prior art method requires that each hole be individually measured, which results in a long cycle time. Also, the use of the distinct machines for determining whether a cooling hole is plugged and for determining the true position of the hole requires that the inspection be performed on distinct platforms.